# Definition:Second Order Fibonacci Number

The second order Fibonacci numbers are a sequence $\sequence {\FF_n}$ of integers which is formally defined recursively for all $n \in \Z_{\ge 0}$ as:
$\FF_n = \begin{cases} 0 & : n = 0 \\ 1 & : n = 1 \\ \FF_{n - 1} + \FF_{n - 2} + F_{n - 2} & : \text{otherwise} \end{cases}$
where $F_{n - 2}$ denotes the $n - 2$th Fibonacci number.